Modulatable frequency oscillation tube arrangement



Patented Dec. 112, 1950 MODULATABLE FREQUENCY OSCILLATION TUBE ARRANGEMENT Albert M. Skellett, Madison, N. J., assignor to National Union Radio Corporation, Orange, N. J a corporation of Delaware Application January 2a, 1948, Serial No. 4,892

14 Claims.

This invention relates to electron tube apparatus and more particularly to arrangements for controlling Or modulating the oscillation frequency of an electron tube oscillator.

A principal object of the invention is to provide an improved electron tube arrangement for generating ultra high frequencies, for example of the order of 200 megacycles or more.

Another object is to provide an improved electron tube oscillation generator which has a special arrangement of electrodes for controlling the generated frequency in response to electron transit time variation.

Another object is to provide an ultra highfrequency oscillation generator tube arrangement which is capable of having its generated frequency varied or controlled over a wide range by means of a relatively low frequency control or modulating signal with a minimum of power consumption in the modulating process.

A feature of the invention relates to a multigrid ultra high-frequency oscillation generator tube having a grid array for more efficiently utilizing variations in electron transit time to vary thereby the generated frequency.

Another feature relates to a modified form of beam power tube for producing a controlled or frequency-modulated ultra high-frequency carrier.

A further feature relates to the novel organization, arrangement and relative location of parts which cooperate to provide an improved ultra high-frequency tube arrangement which will operate over a Wider frequency range while being capable of direct frequency modulation by relatively low frequency signals.

Other features and advantages not particularly enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims.

In the drawing,-

Fig. 1 is a composite structural and schematic wiring diagram of a frequency-controlled oscillation generator according to the invention.

Fig. 2 is an equivalent schematic wiring diagram of Fig. 1.

Fig. 3 is a modification of the tube of Fi 1.

Fig. 4 is a further modification of the tube of Fig. 1.

Fig. 5 is a graph explanatory of the operation of the invention.

Fig. 6 is a schematic block diagram showing the invention embodied in a frequency stabilizing arrangement.

In the field of ultra high-frequency oscillabe connected across grids 4 and 6.

tion generators, it is, desirable to control or modulate the generated frequency by means of a relatively low frequency voltage without appreciable energy consumption in the modulating or control process. One example of such an arrangement is the well-known reflex Klystron tube, wherein the modulation is effected electrostatically. However, where the modulating voltages are at relatively low frequency, considerable difliculty is encountered in the direct modulation of the ultra high-frequency oscillations. The electron tube arrangement according to the invention, provides the desired frequency modulation or control of an ultra high-frequency wave, while allowing the tube to be used to generate such waves over a comparatively wide range. While the invention finds its primary utility in a frequency-modulated radio transmitter, it will be understood that the inventive concept is capable of embodiment in other types of ultra high-frequency equipment. One of the important results obtainable with the present invention is that the ultra high-frequency carrier can be modulated directly in the electron tube, and linearity of frequency swing with respect to input modulating voltage is maintained.

Referring to Fig. l, the electron tubecomprises an enclosing evacuated envelope l of glass or other suitable material within which is supported, in any well-known z..anner no... te header 2, an electrode a"se;nb.y or array according to the invention. This assembly comprises an electron-emitting cathode 3, a series of successive grids 4, 5, 6, I, and a plate or anode 8. While the cathode 3 is shown as of the indirectly heated type having a heater wire 9, it will be understood that a so-called filamentary type cathode may be employed. The grid 4 is arranged to cooperate as a control grid with the anode grid 6 to form a'feedback oscillator. The intervening grid'5 acts as a screen grid. A tuned oscillatory circuit of any well-known type can In Fig. 1, this tuned oscillatory circuit may consist of a tuned wave transmission line comprising the line conductors Ill, H, and capacitance l2. The grid 4 is returned to ground through the radio frequency choke coil i3. Likewise, the cathode 3 is returned to ground through the radio frequency choke coil M. The D. C. biasing poten- IS. The modulating or frequency control potentials are applied at terminals l1, l8 across the cathode 3 and grid I through the radio frequency choke coils I9, 20, which are bridged by condenser 2!. of sufliciently low capacity to keep the generated high frequency oscillations away from terminals I'I, i8, while permitting the low frequency input signals to be impressed on grid I. The screen grid is suitably positively biased with respect to cathode 3. The anode-grid 6 is connected to the positive terminal of the supply source 22 through the radio frequency choke coil l4 and the transmission line conductor ID. The current for heating the cathode is connected to terminals 23, 24. Since the control grid 4 is connected to the line conductor H, the electrodes 3, 4, 5 and 6 act as a conventional tuned-grid, tuned-plate oscillator. The grid 6 is of relatively coarse mesh so as to allow a large fraction of the electrons from cathode 3 to pass therethrough and through grid I to plate 8. Thus the. electrons passing through grid 6 induce corresponding potentials in that grid and in the tuned-grid, tuned-plate circuit.

The grid I on which the low frequency modulating or control potentials are impressed, is negatively biased, for example by bias battery 25 and resistor 26 with respect to cathode 3. The electrons which pass through grid I finally reach the positive plate or anode 8 where they are collected. Since the grids 5 and I and the anode 8 are by-passed to ground, they do not swing in potential with the generated oscillation voltages. On the other hand, the grids 4 and 6 swin in potential with these high frequency oscillations. Consequently, the electrons which pass through grid 4 will be bunched in accordance with the frequency of the oscillations. If we now consider the group of electrons at the peak of the oscillation cycle, they will approach grid 6 and in so doing they will induce a charge on that grid which increases as the electron groups get closer and closer to grid 6. This induced charge will be at a maximum when the electrons are just passing through grid 6, whereafter the induced charge will decrease as the electrons leave grid 6 and pass to grid I. Thus, a pulse of electrons passing from grid 5 to grid I induces a correspondin pulse in the tuned circuit connected to grid 6.

In order to obtain optimum conditions, it is necessary that the electron transit time of the electrons in the two regions of the tube on the opposite sides of grid 6, correspond to a half cycle of the oscillation frequency being generated. That is, it should take approximately one complete cycle of the generated oscillations for the electrons to pass from grid 4 to grid I. By adjusting the various D. C. potentials above described, this electron transit time can be appriately adjusted. If the applied D. C. voltages are not optimum for the desired transit time conditions, the currents induced at grid 6 will not be exactly in phase with the generated oscillations, and therefore the tube will not oscillate as strongly as it would under ideal conditions.

In accordance with the invention, the electrons are brought into and out of. phase with respect to the generated oscillations at grid 6, by controlling the negative voltage applied to grid I. In correspondence with the input or modulatin signals applied to terminals I I, I8, the transit time of the electrons from grid 6 to grid I can be correspondingly varied. At the same time, but to a much smaller extent, the electron transit time between. grids 5 and 6, is

4 varied because of the fact that the field of grid 1 penetrates through grid 6 to a limited extent.

The tuned oscillatory circuit comprised of the transmission line l0, ll, l2, preferably has a relatively broad resonance peak so that it is possible for it to oscillate over a range of frequencies near its resonance frequency. Thus, by varying the phase of the electrons passing through grid 6 with respect to the generated oscillations, as a result of varying the negative potential at grid I, it has been found possible to pull the frequency of the generated oscillations to either side of the resonant point. Since the anode or plate 8 is highly positive and its positive field reaches through the mesh of grid I, it collects the electrons which pass through grids 6 and I. Furthermore, the potential of the region of space in the vicinity of grid 1 is positive even though the potential applied to grid I is negative In other words, the field adjacent grid I is effectively positive in potential to an extent suiiicient to insure the passage of the electrons therethrough to anode 8 and yet this effective positive potential can be varied to vary the transit time by means of a negative voltage applied to grid I. Since the grid is biased negative, no power will be required to change the effective positive potential of the region adjacent grid I and hence no power will be required to effect frequency modulation or control. In other words, the grid I i located in a region between anode 8 and grid 6 which region is at an effective positive potential but the grid I has applied thereto negative external voltages for transit time control purposes as above described.

Fig. 5 is a graph of an actual frequency run obtained with the arrangement shown in Figs. 1 and 2. It will be seen that the variation in frequency of the oscillations is linear over a range'of approximately 'I megacycles at a fundamental frequency at about 227 megacycles. It will be observed that since the modulating voltages applied to grid I throughout the entire range of frequency variation are negative, the modulation is accompanied by no power consumption.

Fig. 3 shows in transverse horizontal section a structural modification of the tube of Fig. 1. In this embodiment, the evacuated enclosing envelope 2'! has on the interior thereof an electrode assembly, comprising a central electron-emitting cathode 28, a first grid 29, a second grid 30, an electrode 3! having windows 32, 33, in opposite sides thereof in longitudinal alignment with the cathode 29, and an additional box-like electrode 34. Mounted between the cathode and the grids 29 and 30 are beam-forming plates 35, 36. The grids 29 and 30 may each be of the type employing a pair of side rods around which are wound the usual fine wire grid laterals, and arranged so that the grid laterals of both grids are in planar alignment, thus tending to form the electrons from cathode 28 into beams extending from the cathode 28 towards the electrode 34. To confine the angular width of these beams, the plates 35 and 36 are connected to the cathode 28, with the result that the electron beams from the cathode 28 are of substantially the same width as the respective windows 32 and 33. To this extent therefore, the tube of Fig. 3 is structurally similar to the well-known beam power tube such as bears the Radio Manufacturers Association designation 6L6. However, the tube of Fig. 3 is so arranged that the electrode 34, which would ordinarily be the output arode, is connected to the signal input circuit so as to have its negative D. C. potential varied in accordance with the signal variations. The electrodes 28, 29 and 3|, are connected so as to form an oscillator generator, and the grid 33 can be connected to a suitable intermediate .positive D. C. potential to cause it to act as a screen grid.

A typical circuit arrangement is shown in Fig. 3A. The tuned oscillatory circuit comprising the inductance 31 and the condenser 38 is connected across the control grid 23 and its cooperating oscillator anode 3|. The electrode 34 is negatively biased with respect to the cathode, and the modulating potentials. are applied to terminals 39, 40, so as to vary the negative potential of electrode 34. Electrode 34 therefore acts as a repeller electrode for the electrons which pass through the windows 32 and 33. A suitable point on inductance 31 is connected to the positive terminal of the plate power supply 4|, so that the electrodes 28, 29 and 3| act as an ultra high frequency oscillator. By means of the variationin the negative D. 0. potential applied to plate 34,

the transit time of the electrons between electrodes 30, 3|, and 3| to 34, and back to 3| can be varied, thus varying the phase of the generated oscillations at electrode 3| with respect to the induced charge on this electrode resulting from the electron beam passing through windows 32 and 33. By this arrangement, it is possible directly to frequency modulate the oscillations generated in the tube between electrodes 28, 29' and 3|, and these frequency-modulated oscillations can be taken off by a suitable coupling coil 42 coupled to the inductance 31.

Fig. 4 shows a modification of Fig. 1, wherein the tube is of the type employing an electron gun construction such as is conventionally employed in cathode-ray tubes. The various elements which correspond functionally to those of Figs. 1 and 2, are designated by the same numerals with the suffix a. In this embodiment, the electrons are emitted from the thermionic cathode 3a. and pass through a central opening in the cup-like metal grid electrode 40. from whence they pass through a corresponding central opening in the metal disc grid a. Electrode 6a. is in the form of a metal cylinder. Thus the electrons from the cathode are substantially focussed. in a beam passing through the electrodes 4a, 5a and 6a,-and thence through the grid 10. to the anode Ba. If desired, separate magnetic field means (not shown) may be provided for keeping the electrons in a focussed beam as is well-known in the cathode-ray tube art. In the embodiment of Fig. 4, the electrode 6a. does not collect any electrons but otherwise it functions similarly to the electrode 6 of Figs. 1 and 2. The circuit connections for the various electrbdes for the tube of Fig. 4 may be the same as those of Figs. 1 and 2. Thus, the input signals applied to grid 'Iavary the efiective positive potential in-the region of grid la and thus vary the electron transit time between grid 4a and electrode 60., as well as the electron transit time between electrode 6a and grid la. By suitable adjustment of the various biasing voltages applied to the electrodes as described above in connection with Figs. 1 and 2, the charges which are induced on the electrode 6a by the passage of the electrons therethrough, can be brought into phase with the generated oscillations, and as above described the variation in transit time effected by the signals applied to grid 1a correspondingly varies the frequency of these generated oscillations.

While in the foregoing, the invention has been described as used for the purpose of frequencymodulating an ultra high-frequency carrier, it will be understood that the invention can be used for the purpose of controlling or stabilizing a generated frequency. Thus, there is shown in Fig. 6, a typical superheterodyne radio receiving system comprising the usual radio frequency amplifier 43. a frequency mixer or converter stage 44 for mixing the amplified received signals with local oscillations generated in the oscillator tube 45. The tube 45 and its associated circuits may be identical with any of the embodiments illustrated in Figs. 1, 2 and 4. In accordance with the foregoing description, the grid is normally negatively biased so that the tube 45 generates the local heterodyning signal at the desired frequency. The output of the converter 44 is then amplified in a suitable intermediate frequency amplifier 4B and the intermediate frequency signal can then be detected in any suit- ..abledetector 41 and applied to an audio amplifier'48, and thence to a reproducer 49. A portion of the intermediate frequency output from amplifier 46 is rectified in a suitable rectifier 50 and thence passed through a filter 5| to apply the proper negative D. C. biasing potential to the grid 1; If for any reason the oscillator tube 45 should drift in frequency, the magnitude of the control signal applied to grid 1, will likewise automatically vary and will restore the generated oscillations to their proper frequency by controlling the transit time of the electrons from cathode 3 as they reach grid 6.

While certain particular embodiments have been described herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is: I

1. Electron tube apparatus for generating oscillations of a controllable frequency, comprising an evacuated envelope containing a cathode, an anode, and a pair of cooperating electrodes for generating ultra-high-frequency oscillations by feedback action therebetween, one of' said pair of electrodes having potentials induced therein by reason of electrons passing it, a negatively biased grid between said pair of electrodes and said anode, and means to vary the negative bias on said grid to vary the electron transit time of the electrons. reaching the second of said pair of electrodes in correlation with the periodicity of said generated oscillations and thereby to vary the frequency of the generated oscillations.

2. Electron tube apparatus for generating oscillations of a controllable frequency, comprising an evacuated envelope containing a cathode, an oscillator control grid, and an oscillator anodegrid, a tuned oscillatory circuit connected to said control grid and to said anode-grid for the generation of ultra-high-frequency oscillations by feedback action therebetween, an output 7 anode, and; means to vary the electron transit time'of the electrons passing through said anodegrid to correlate said transit time with the periodicity of said oscillations and thereby to vary the frequency or thegenerated oscillations, the last-mentioned means including a normally negatively biased grid located between said anode-grid and said output anode.

3. Electron tube apparatus for generating oscillations of controllable frequency, comprising an evacuated envelope containing a cathode and an anode; and in sequence between the cathode and anode, a control grid, an anode-grid, and a frequency control grid; a tuned oscillatory circuit connected to said cathode, control grid, and anode-grid, to generate ultra-high-frequency oscillations by feedback action therebetween; and means to vary the negative direct current potential on said frequency control grid to correlate the transit time of the electrons with respect to their arrival at said anode-grid with the frequency of said oscillations to vary thereby the frequency of the generated oscillations.

4. Electron tube apparatus for producing a frequency-modulated ultra-high frequency carrier, comprising an evacuated envelope containing an electron-emitting cathode, an electron collector anode, an oscillator generator control grid and an oscillator generator anode-grid located between said cathode and collector anode, a tuned oscillatory circuit connected to said control grid and to said anode-grid to generate ultra-high-frequency oscillations by feedback action therebetween, said anode-grid having electric charges induced thereon in correspondence with the electrons passing therethrough, and means to vary the transit time of the electrons between said control grid and said anodegrid, the last-mentioned means including an additional grid located between said anode-grid and said collector anode, said additional grid being normally negatively biassed with respect to the cathode'and having its negative direct current potential varied by the modulating signals applied thereto.

5. Electron tube apparatus for producing a frequency-modulated ultra-high-frequency carrier, comprising an evacuated enclosing envelope containing an electron-emitting cathode, an oscillator generator grid, an oscillator generator anode-grid, a tuned oscillator circuit connected to said control grid and said anode-grid for generating ultra high frequency oscillations, said anode-grid having charges induced thereon at the frequency of said oscillations in response to electrons passing through said anode grid, an output anode, an additional grid between said anode-grid and said output anode and located in a region where the field between the cathode and anode has a positive potential gradient, means normally biassing said additional grid negatively with respect to the cathode, and means to vary said negative bias to thereby modulate the frequency of the generated oscillations.

6. Apparatus for generating a frequency-modulated ultra-high-frequency carrier, comprising a source of frequency-modulating signals, an evacuated envelope containing an electron-emitting cathode and an electron collector anode; and in sequence between the cathode and collector anode, an oscillator generator grid, an oscillator generator anode-grid said generator-grid and said anode-grid being interconnected to generate ultra high frequency oscillations therebetween, and a transit time control grid upon which the frequency-modulating signals are impressed to vary the transit time of the electrons with respect to said anode-grid and thereby to vary the frequency of the generated oscillations.

'7. An electron tube according to claim 6, in which the said transit time control grid is normall negatively biassed and the modulating signals are applied to var the said negative bias.

8. An electron tube according to claim 6, in which a shield grid is located between said oscillator control grid and said oscillator anode.

9. Electron tube apparatus for generating frequency-modulated ultra-high-frequency carrier, comprising an electron gun for developing an electron beam, an oscillator generator control grid through which the beam passes, an oscillator generator anode through which the beam passes, said grid and anode being interconnected to generate ultra high frequency oscillations therebetween a tuned oscillatory circuit connected to said grid and anode, an electron collector output anode, and a grid electrode located between said oscillator anode and said collector anode to correlate the transit time of electrons between said oscillator control grid and said oscillator anode and thereby to vary the frequency of the generated oscillations.

10. Electron tube apparatus for generating a frequency-modulated ultra-high-frequency carrier, comprising an electron-emitting cathode, an oscillator generator grid, an oscillator generator anode, said grid and anode being interconnected to generate ultra high frequency oscillations therebetween said anode having at least one electron permeable window, electron beam forming means for causing the beamed electrons to pass through said window, an electron repeller electrode for repelling electrons after passage through said Window, a tuned oscillatory circuit connected to said oscillator grid and oscillator anode to generate ultra-high-frequency oscillatons, and means to vary the negative potential on said repeller electrode in accordance with modulatingv signals to correlate the transit time of the electrons with respect to said generatoranode and with the periodicity of the generated oscillations and thereby to directly vary the frequency of said generated oscillations.

11. Electronic frequency control apparatus comprising an oscillator generator tube whose frequency is to be controlled, said tube comprising an evacuated envelope containing a cathode, an output anode, an oscillator generator control grid, an oscillator generator anode-grid, a tuned oscillatory circuit connected to said control grid and said anode-grid for generating ultra-high-frequency oscillations, said anodegrid having charges induced therein at the fre-- quency of said oscillations in response to electrons passing through said anode-grid, an additional grid between said anode-grid and said output anode and located in a region where the field between the cathode and anode has a positive potential gradient, circuit arrangements for mixing the generated oscillations from said tube with other oscillations to produce a control frequency, means to rectify said control frequency to produce a negative bias for application to said additional grid and thereby automatically maintaining the oscillations generated by said tube at a predetermined frequency.

12. Frequency modulation apparatus, comprising an evacuated bulb having an electronemitting cathode, first and second grids successively traversed b the electrons from said cathode, resonant circuit means interconnecting said grids and said cathode to generate high frequency oscillations within the tube, an output anode to receive the electrons from said cathode,

- a third grid located between said grid and said essence cordence with signal modulations to vary the transit time of the electrons from the cathode with respect to said second grid and thereby to vary directly the frequency of the generated oscillations.

13. Frequency modulation apparatus, comprising an evacuated tube including an output anode, an electron-emitting cathode for producing an electron stream between said cathode and said anode, first, second. and third grids located be tween said cathode and anode and successively traversed by said electron stream, a resonant circuit interconnecting the first and second grids to generate ultra high frequency oscillations in said electron stream, means normally negatively hiassing the third grid to correlate the electron transit time between the first and third grids with one complete cycle of the generated oscil-= latiens, and means to vary said negative bias under control modulating signals to vary said time end thereby to directly vary the frequency generated oscillations.

and third grids each corresponds to a h" of the generated oscillation frequency.

ALBERT M. REFERENCES (CIIZI'IEL'D The following references are of recorfile of this patent:

UNITED STATES Prim ii? Number Name 2,3933% Brown J 2,397,822 Van Den Bosch A 2,401,945 Linder June 2,425,657 Tunick a. hug 2,434,104 Kroger J 2,435,601 

